Cops & Robbers is a certain pursuit-evasion game between two players, Alice and Bob. Alice is in charge of the Justice Bureau, which controls one or more law enforcement officers, the cops. Bob controls a single robber, a guy whose main concern is to evade the cops at any costs. Both deploy their guys on the vertices of a city, a simple graph, and start a manhunt under the following natural rules:
On her turn, Alice chooses a (possibly empty) subset of the cops and moves them to some adjacent vertices.
On his turn, Bob may either move his robber to an adjacent vertex or stand still.
The game ends with a win for Alice whenever any of her cops manages to occupy the same vertex as the robber. Bob wins if this never happens in the game.